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Ann Surg. Nov 2000; 232(5): 704–709.
PMCID: PMC1421225

Impact of Race on the Outcome of Carotid Endarterectomy

A Population-Based Analysis of 9,842 Recent Elective Procedures

Abstract

Objective

To examine the influence of race and other potentially confounding variables on the outcome of carotid endarterectomy (CEA).

Summary

Previous studies have demonstrated that CEA is performed less frequently in black patients, although little attention has been focused on the influence of race on the outcome of surgery.

Methods

The Maryland Health Services Cost Review Commission database was reviewed to identify all elective CEA procedures performed in all nonfederal acute care hospitals in the state from 1990 through 1995 to examine the influence of race and other factors on the rates of in-hospital complications, in-hospital stroke, length of stay, and total hospital charges.

Results

Carotid endarterectomy was performed in 9,219 (94%) white and 623 (6%) black patients during this period. The in-hospital stroke rate was 1.7%—3.1% among black patients and 1.6% among white patients. Black patients had a longer length of stay and higher mean hospital charges than white patients. Multivariate logistic regression analysis identified black race as an independent risk factor for in-hospital stroke. Performance of CEA by a high-volume surgeon was protective for the combined occurrence of in-hospital stroke or death, and whites were more than twice as likely to undergo surgery performed by high-volume surgeons. Conversely, undergoing surgery in a low-volume hospital was associated with in-hospital stroke, and blacks were four times as likely to use low-volume hospitals.

Conclusions

Black patients who underwent elective CEA in Maryland from 1990 to 1995 had an increased incidence of in-hospital stroke, a longer hospital stay, and higher hospital charges than whites. Black race was identified as an independent risk factor for in-hospital stroke, although the reasons for this influence of race on outcome are undefined. The authors’ observations also suggest the possibility of limited access to optimal surgical care among blacks, and this issue warrants further study.

Each year, stroke affects more than 500,000 persons in the United States, resulting in a significant number of deaths and permanent physical disability. 1 Because extracranial carotid artery arteriosclerotic occlusive disease is a common cause of ischemic stroke, it is not surprising that carotid endarterectomy (CEA) is the most frequently performed peripheral vascular surgical procedure in this country. 2 However, although the incidence of death from stroke is increased in blacks, 3,4 previous community-based studies have demonstrated that blacks are much less likely than whites to undergo this stroke-preventing surgical procedure. 5–8 Although the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and the Asymptomatic Carotid Atherosclerosis Study (ACAS) demonstrated the superiority of CEA over the medical management of patients with symptomatic and asymptomatic carotid artery stenoses, respectively, approximately 95% of the patients included in these trials were white, and the impact of race on surgical outcome was not measured. 9,10 In a previous study, we examined the influence of patient age and hospital CEA volume on the outcome of the procedure in Maryland. 11 The current analysis was undertaken to examine the influence of race and other potentially confounding demographic variables on the outcome of CEA.

METHODS

The Maryland Health Services Cost Review Commission database was reviewed to identify all elective CEA procedures performed from 1990 through 1995 in all nonfederal acute care hospitals in the state using a previously reported algorithm, including a combination of search codes based on the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) code 38.12 (endarterectomy of the vessels of the head and neck other than intracranial vessels) in the primary but not in any secondary position, the presence of diagnosis code 433–433.91 (occlusion/stenosis, precerebral artery), and the Diagnosis-Related Group (DRG) 5 (extracranial vascular procedure). 11 Patient variables analyzed included age; race; gender; payment source, including Medicare, Medicaid, and commercial; hypertension (ICD-9-CM codes 401–405); diabetes mellitus (250); heart disease (391, 394–398, 402, 404, 411–414, 416, or 425); chronic pulmonary disease (COPD) (415.0, 416.8–416.9, 491–494, or 496); renal disease (585–586, V42.0, V45.1, or V56); and indications for surgery including previous stroke (342 or 438), transient ischemic attack (435 or 781.4), and amaurosis fugax (362.34 or 368.12). Patients were considered asymptomatic if there was no history of stroke, transient ischemic attacks, or amaurosis fugax. These clinical diagnoses were identified using codes from the Romano adaptation for administrative databases of the Charlson comorbidity index. 12,13

Outcomes measured were in-hospital death, determined from the Maryland Health Services Cost Review Commission discharge status field; in-hospital stroke (diagnostic code 997.0: surgical complication, central nervous system); hospital length of stay (LOS); and total hospital charges. Hospitals were classified as performing a very low (<15), low (15–29), moderate (30–49), or high (≥50) volume of procedures annually. Individual surgeons were classified as performing a very low (1–4), low (5–14), moderate (15–29), or high (≥30) volume of procedures annually.

Categorical variables, such as gender, payment source, hypertension, diabetes mellitus, COPD, renal disease, heart disease, and surgical indications, were analyzed by chi-square analysis. Continuous variables such as age, average LOS, average total charges, and specific service charges were analyzed by the Mann-Whitney test. The influence of age, race, gender, annual hospital volume, annual surgeon volume, payment source, and other demographic variables on the incidence of perioperative stroke, in-hospital death, and combined stroke and death was each examined by multiple logistic regression analysis. In each of the three models, the presence of a comorbidity was indicated by a dichotomous variable (i.e., hypertension, diabetes mellitus, COPD, renal disease, heart disease). Dummy variables were created for payment source, hospital volume, and surgeon volume because these variables have more than two levels of categories. In all three models, commercial payment source was used as the baseline against which the payor results were interpreted. Similarly, the very low hospital volume group (1–15 cases annually) and the very low surgeon volume group (1–4 cases annually) were selected to be the comparison groups in the logistic models for the hospital and surgeon volume variables, respectively.

RESULTS

From January 1990 through December 1995, 9,918 elective CEA procedures were performed in 48 (92%) of the 52 acute, nonfederal hospitals in the state. In 9,842 (99.2%) cases, the patient’s race was coded as white or black, and these patients formed the basis of this study. The other 76 cases, in which the patient was classified as Asian/Pacific Islander, American Indian/Eskimo, other, or unknown, were excluded from the analysis.

Carotid endarterectomy was performed in 623 (6.3%) black and 9,219 (93.7%) white patients. Black patients were younger than white patients (mean age 66.8±9.4 vs. 69.4±8.6 years, P < .0001). There was a significantly greater prevalence of hypertension, diabetes mellitus, and renal disease among blacks, although COPD was significantly more common in whites (Table 1). The indication for surgery was symptomatic disease in 17.8% of whites and 20.5% of blacks (P = .094). Amaurosis fugax was a more common indication in whites; previous stroke was a more common indication in blacks. CEA was performed in 5,397 (54.8%) men and 4,445 (45.2%) women; 57.9% of the black patients and only 44.3% of the white patients were women (P < .0001).

Table thumbnail
Table 1. DEMOGRAPHICS

Payment source analysis revealed that 71.3% of the whites and 61.8% of the blacks were Medicare beneficiaries (P < .0001), and 1.6% of the whites and 9.8% of the blacks were Medicaid beneficiaries (P < .0001).

As noted in Table 2, white patients were almost twice as likely as black patients to undergo surgery at a high-volume hospital (P < .001) and more than twice as likely to have their surgery performed by a high-volume surgeon (P < .001). In contrast, black patients were four times as likely to use a very low-volume hospital (P < .001) and almost twice as likely to have their surgery performed by a very low-volume surgeon (P < .001) than white patients.

Table thumbnail
Table 2. HOSPITAL AND SURGEON CASE VOLUME

The in-hospital stroke rate was 3.1% among blacks and 1.6% among whites (P = .006). As noted in Table 3, black men and women had a higher in-hospital stroke rate than their white counterparts. The in-hospital death rate was 0.9% and was similar for blacks and whites.

Table thumbnail
Table 3. PERIOPERATIVE DEATHS AND STROKES

Logistic regression analysis identified black race as an independent risk factor for in-hospital stroke (P = .048). Undergoing surgery at either a low-volume or a moderate-volume hospital, as opposed to a very-low-volume hospital, was protective for the development of in-hospital stroke (P = .005 and P = .002, respectively) (Table 4). As noted in Table 5, heart disease (P < .001) and diabetes (P = .024) were predictive of in-hospital death, but black race was not. However, hypertension (P < .001) was protective for in-hospital death. When the outcomes of in-hospital stroke and death were combined, heart disease (P = .001) was an independent risk factor, but race was not (Table 6). Having a high-volume surgeon was found to be protective for either in-hospital stroke or death (P = .046). Hypertension was shown to be negatively associated with the two outcomes of interest (P = .006).

Table thumbnail
Table 4. LOGISTIC REGRESSION ANALYSIS: PERIOPERATIVE STROKE
Table thumbnail
Table 5. LOGISTIC REGRESSION ANALYSIS: PERIOPERATIVE DEATH
Table thumbnail
Table 6. LOGISTIC REGRESSION ANALYSIS: PERIOPERATIVE DEATH OR STROKE

Race was observed to have a significant impact on the economic outcome of surgery. As noted in Table 7, blacks had a mean LOS 2.3 days longer than whites (P < .0001), and mean hospital charges were 49% higher among blacks (P < .0001). The increased economic burden incurred by black patients included all components of the total hospital bill.

Table thumbnail
Table 7. LENGTH OF STAY AND ECONOMIC OUTCOMES

DISCUSSION

Previous studies have demonstrated that blacks have a higher rate of cardiovascular death, 3,14 ischemic stroke, 7 and death from stroke 4,6,7,15 than whites. Despite this, little attention has been paid to the impact of race on the outcome of CEA. The current study is the first statewide analysis of this issue, and it demonstrated that blacks had a 94% increased incidence of in-hospital stroke compared with whites, but an equivalent in-hospital death rate. Further, logistic regression analysis identified black race as an independent risk factor for in-hospital stroke after CEA. Because several potentially confounding variables were included in this multivariate analysis, the explanation for this influence of race on outcome is unsettled.

Our findings conflict with the results of two other recent investigations. In a report of 1,160 patients undergoing CEA at 12 academic medical centers, the rate of perioperative complications was not influenced by race. 16 However, the latter study included only patients with preoperative symptoms and may have included urgent or emergent operations, two variables known to be associated with an increased rate of perioperative complications. Thus, the perioperative stroke and death rate of 5.7%, which is considerably higher than in the Maryland experience, may have masked any potential influence of race on outcome. 16 In the current study, most of the patients underwent surgery for asymptomatic carotid disease. Further, our analysis captured all elective procedures performed in the state, including the broad spectrum of both academic and community hospitals, in both urban and less populated locales, and therefore may be more representative of the outcome of this procedure across the country in general.

In a review of the Medicare database, Hsia et al 17 reported an increased rate of surgical death among blacks undergoing CEA. However, that analysis may have excluded a significant number of blacks because, as noted in the present study, blacks tend to be younger than whites and are less often Medicare beneficiaries at the time of CEA (see Table 1). In addition, that study used only ICD-9-CM code 38.12 to identify CEA cases. Previous work has demonstrated that by using this single code, one may capture procedures performed either synchronously, or staged, with cardiac surgical procedures, or urgent/emergent procedures, thus resulting in a higher rate of perioperative complications. 11 The methodology used in the present study excluded that subset of cases but did include all solitary, elective procedures performed, irrespective of patient age or payment source.

There are several potential pathologic, clinical, and epidemiologic explanations for the higher perioperative stroke rate experienced by blacks in Maryland. For example, a greater prevalence of intracranial arteriosclerotic lesions has been identified among blacks in both autopsy 18,19 and angiographic investigations. 4,20–24 However, recent studies suggest that intracranial disease does not significantly increase the risk of surgery. 24–28 Unfortunately, preoperative angiographic findings are not available in this database. Hypertension occurred significantly more often among blacks undergoing CEA in Maryland, consistent with the greater prevalence of this condition in the black population in general. 3,29 However, in a recent study, hypertension was not associated with a higher CEA stroke rate. 30 Similarly, patients with diabetes have 2.5 times the stroke incidence of patients without diabetes, 31 and the prevalence of diabetes was significantly greater in blacks than in whites in this study. However, in a recent analysis of 732 patients who underwent CEA, including 284 (39%) with a history of diabetes mellitus, the patients with diabetes had no increased incidence of perioperative neurologic complications. 32 It is not surprising, therefore, that diabetes mellitus was not identified by logistic regression analysis to be associated with in-hospital stroke in the current population-based study.

However, the incidence of perioperative stroke correlates with the clinical indication for surgery and is lowest among patients who were asymptomatic before surgery. The relatively low in-hospital stroke rate noted in this statewide analysis may reflect, at least in part, the high incidence of asymptomatic patients. Although the current analysis demonstrated variability in the specific symptomatic indications for surgery between white and black patients (see Table 1), there was no difference in the overall incidence of symptomatic versus asymptomatic disease between white and black patients. Previous work has also failed to demonstrate a greater incidence of symptomatic disease among black patients undergoing CEA. 33

Other researchers have demonstrated an inverse correlation between the incidence of perioperative complications and annual CEA volume. 34,35 The current analysis, which controlled for a variety of potentially confounding variables, confirmed that undergoing CEA at a very-low-volume hospital was associated with in-hospital stroke compared to high- and moderate-volume hospitals, and blacks were four times as likely to undergo surgery at the very-low-volume institutions. Further, performance of the procedure by a high-volume surgeon was protective for the development of in-hospital stroke or death, and black patients were significantly less often treated by high-volume surgeons. However, because hospital and surgeon volume were included in our logistic regression analysis, other unidentified factors may be responsible for the increased in-hospital stroke rate experienced by blacks undergoing CEA in Maryland.

In contrast, previous research demonstrated an inverse correlation between annual hospital CEA caseload and LOS and charges. 11 It is therefore not surprising, because blacks were much more likely to undergo CEA in low-volume hospitals, that LOS and charges were significantly higher among blacks than whites (see Table 7). Because a significantly greater percentage of black patients were Medicaid beneficiaries, these epidemiologic observations raise the possibility of limited access to optimal carotid surgical care among the black population, as has been demonstrated with respect to other specialized therapeutic interventions. 36–38

The question of unequal access to optimal surgical care is particularly worrisome in view of the infrequency with which CEA is performed in black patients in Maryland, as elsewhere. The relative underperformance of this procedure among blacks has traditionally been attributed to the increased prevalence of intracranial, 18,21,23 and the decreased prevalence of extracranial, 21,22,38–41 cerebrovascular occlusive disease among this patient population. However, during the past several years, the presence of intracranial (so-called tandem) lesions has not been considered a significant contraindication to performing CEA in patients with otherwise appropriate surgical indications. 26–28 Further, several recent studies have failed to detect a higher incidence of extracranial disease among whites. 4,19,42,43

Based on an analysis of the Veterans Affairs database, Oddone et al 7 postulated that the underperformance of CEA among blacks may reflect a referral bias based on a perception of increased procedural risk. The findings of the present study indicate that this perception may be accurate and may explain the reluctance of some clinicians to refer black patients for this procedure, or of many patients to accept that recommendation. Although the NASCET and ACAS data provide compelling evidence of the safety and efficacy of CEA, because blacks constituted only a small minority of the patient populations in these trials, the current observations suggest that it may not be valid to extrapolate those findings to black patients with significant carotid disease. 9,10 One must be cautious in analyzing the influence of comorbid factors, as recorded in any large statewide database, on surgical outcome because of inherent potential coding imprecision. Clearly, this may have limited our ability to identify specific clinicopathologic reasons for the poorer outcome experienced by black patients in Maryland. However, in NASCET and ACAS the procedures were performed by a select group of high-volume surgeons, and in high-volume centers. We were surprised to find that in Maryland, black patients were significantly more likely to undergo CEA in very-low-volume hospitals and were much less likely to have a high-volume surgeon. These epidemiologic observations, the relatively infrequent performance of this common procedure in blacks, and the higher complication rate and costs experienced by this patient population should serve as a stimulus for further investigation of this issue.

Footnotes

Correspondence: Bruce A. Perler, MD, Dept. of Surgery, Harvey G11, The Johns Hopkins Hospital, 600 N. Wolfe St., Baltimore, MD, 21287-8611.

E-mail: Bperler@jhmi.edu

Accepted for publication December 27, 1999.

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